yada yada yada

Introduction

People are always bothering me with their guitar pedals they think they have fried. What have they done almost every time this happens? They've used a random power supply and now their pedal wont turn on. They haven't realised (or at least appreciated) that there are a number of differences between power supplies, some of which can have very negative consequences if recklessly inserted into the wrong hole. [P.S. If you're in this situation right now, the pedal is very often salvageable with little effort, but that's for another post]

Recently a friend of mine in their 50's, who runs a successful recording studio no less, asked me which power supply they needed to get to replace a broken one. WTF dude!?

If they were unsure which power supply to use, I realised there must be a lot of confusion around this issue, so it motivated me to throw together this blog post to perhaps reduce the overall angst in the universe a tiny fraction. As I go through I will parse only the relevant information starting at the potentially most lethal, moving through to the least.

Standard DC Power Supply From a Well-Known Guitar Pedal Manufacturer

Standard DC Power Supply From a Well-Known Guitar Pedal Manufacturer

lots of markings, numbers and pictures

Looking at the markings of a power supply it is actually quite apparent why there is so much confusion. First off, there is a lot of unnecessary "decorative" information mixed with technical info, and some of it is even rendered in hieroglyphics. ​Below is the same images as above but with all unnecessary information (at least for our purposes) removed.

Standard DC Power Supply From a Well-Known Guitar Pedal Manufacturer with all the Nonsense Removed

Standard DC Power Supply From a Well-Known Guitar Pedal Manufacturer with all the Nonsense Removed

input jack polarity

Centre Positive Symbol

Centre Negative Symbol

These ancient fertility symbols have been appropriated by electronics manufacturers to represent the polarity of the input jack. The section that is doing the impregnating represents the polarity of the 'centre' contact (the contact on the inside of the input jack). So, on the left image we have a centre positive jack and on the right we have a centre negative jack.

2.1mm Power Supply Input Jack

Get the polarity of the input jack wrong and things will go one of two ways: if you are lucky you will ​justfry the reverse polarity protection in your circuit; or unlucky and fry the main circuit of your device. Don't get this wrong.​

Output signal

There are a number of elements we have to be aware of with the output:

- CURRENT TYPE (DC or AC)- VOLTAGE- CURRENT DRAW LIMIT

CURRENT TYPEWe have two options here: AC (alternating current) or DC (direct current). On the image of the power supply on the left we can see the manufacturer has clearly marked DC. However, on the right image we again have a symbol: A dash with three smaller dashes below it. This symbol represents DC. There is also a symbol for AC: a sine wave (see below).

Using an AC adaptor where a DC is expected will have a similar effect on your circuit to getting the polarity of the input jack wrong. DC where AC was expected probably won't have a detrimental effect although the device may appear to light up but not work.

AC & DC Symbols

VOLTAGEThis is the output voltage of the adaptor. Too low and your device won't operate properly. Too high and it could fry sensitive components.

CURRENT DRAW LIMITOur adaptor on the left is rated for 100mA and the right 200mA. This is how much current you can draw from the adaptor. If this value is too low, your device won't be able to draw enough current to work. It's fine to over estimate this value.​

INPUT SIGNAL

The power into your adaptor, which will be plugged into mains power supply, is going to be AC (note the symbol on the right).

​Our adaptor on the left is rated for American flavoured electricity (120V, 60Hz) and the one on the right UK flavoured (240V, 50Hz). Other regions around the world have their own voltages and frequencies and it is important that your adaptor is designed for your region so that it adapts the electricity into the form it says it will. This is particularly important if you trying to get DC power and want to prevent mains hum getting into your signal path.

outro

So I hope that's clear and helpful. If you're not sure which power supply your device needs check the manufacturer's manual or do a google search. Resit the urge to just 'give it a shot'!

So a friend of mine came to me in a panic. She was building a clone of a very high-end rack mount compressor, and in the process of desoldering some wires from the main PCB, she had left the solder pads unfit for purpose. There was wire lodged in all three holes and one of the traces had started to lift. As this was for a final year college project, there was much anxiety and possibly tears.​

The aftermath of a poorly executed desoldering job amongst some very pretty soldering work

The fix

Fortunately (and this is usually the case with most PCBs and stripboard projects) there is a very simple fix/workaround.

​So if you find yourself in my friends position, what you need to do is to simply give up on these solder pads. Any further heating or abuse could lead to the traces coming up and affecting solder pads near by.

To carry out the work-around you need to follow the traces under the board (the lines that are slightly raised from the surface of the PCB) to another solder pad and solder to that. Simple.​

As you can see from the image above there are alternative positions for soldering each of the three wires.

If these were through-hole components with legs that needed soldered to (and the solder pads are now unusable), first clear the holes of the solder pads by heating with a soldering iron on one side of the PCB and using the desolder pump on the other side. With the holes now clear, place the component through and solder a wire from the leg to the alternative soldering position.

When you understand how PCBs and electrical connections work, this work around seems extremely obvious. However, I know it's a stress that many people starting out in electronics have experienced so I felt it was a worthwhile topic to post on.​

better desoldering

Life would have been easier for my friend if she had done a couple of things. So if you are starting out working on DIY electronics projects, this would be my advice:

- Use (high-grade, fast flow) leaded solder- Remember the "heat on one side of the PCB, desolder pump on the other" trick to clear solder from inside a pad.- Use a decent metal desolder pump.- Don't get worked up! If it's frustrating you, take a break, stare at kittens on the internet for a while, then come back to it. - Read-up on how PCBs work and deepen your understanding of electrical connections.

And finally, please always remember: Don't Panic! It's very rare you've truly destroyed your DIY electronics project. There are always more components and decades of troubleshooting that have led to plenty of workarounds.

We recently released our first few modular synth DIY kits, which are available at the minute on this site and also over at Thonk [link]. The kits are in the Eurorack format, and are the first of a set modules that can be built as individual DIY kits to form a versatile, portable and gnarly sounding synth. ​

Each kit features a detailed, full colour, illustrated assembly guide. The assembly guide walks through the kit build in a step by step process, with pictures and descriptions of the components at each step. The guides also include a schematic diagram, and a description of what's happening in the circuit.​

check out one of our assembly guides: LVLS

We've published the Assembly Guides under a Creative Commons Attribution, Share Alike 4.0 International Licence, so you could for example take different parts from different schematics to combine or build into your own synth DIY circuits or breadboard creations, or, if you want to change the gain in your pre-amp, you can check the schematic and circuit description to figure out which resistor to change on the PCB.

But I haven't soldered before, we hear you whisper! The module designs are also adapted for an introductory level soldering from a couple of other viewpoints including for example adapted component solder pad sizes, and easy to read PCB silkscreens. If you feel like a bit of chat and banter when you're building your first kit, then pop along to one of our regular synth DIY workshops, where we run through everything slowly and step by step in a relaxed environment.

As there is a wide and varied range of modules in the Eurorack format, ranging from tiny 1HP passive modules to almost complete synth voices in one module, and as our modules are compatible with modules from any other Eurorack designers or makers, this allows for many different sound design and creative signal processing possibilities!

Author

We have lots of people writing for us who are interested in making, creative technologies, music, the maker movement and everything inbetween. If you'd like to contribute we'd be delighted! You can contact us on blog@maker.ie.